In recent years, together with development of compact information devices, downsizing of electronic components to be installed thereon have rapidly been progressed. In order to meet the downsizing requirement, a ball grid array (hereinafter, referred to as “BGA”), in which electrodes are provided on a back surface thereof, is applied to an electronic component to cope with the small and narrow connection terminal or the reduced mounting area.
As an electronic component to which the BGA is applied, for example, a semiconductor package is exemplified. In the semiconductor package, a semiconductor chip having electrodes is sealed with a resin. On the electrodes of the semiconductor chip, solder bumps are formed. The solder bumps are formed by joining solder balls to the electrodes of the semiconductor chip. The semiconductor package to which the BGA is applied is mounted on a printed circuit board by joining the solder bumps melted by heating to conductive lands of the printed circuit board. Further, in order to meet the higher-density mounting requirement, a three-dimensional high-density mounting has been developed in which semiconductor packages are stacked in the height direction.
However, when a BGA is applied to a semiconductor package in which the three-dimensional high-density mounting is used, there is a case where solder balls are collapsed by the weight of the semiconductor package itself. If such an accident happens, an appropriate space cannot be maintained between substrates.
Thus, a solder bump has been studied which is formed by electrically connecting a Cu ball, a Cu core ball or the like to the electrode of an electronic component with the use of solder paste. Such solder bumps formed by using Cu balls can support a semiconductor package by the Cu balls or the like, which are not melted at the melting point of solder, even when the solder bumps receive the weight of the semiconductor package in mounting the electronic components on the printed circuit board. Therefore, the solder bumps are not collapsed by the weight of the semiconductor package itself. Here, the Cu core ball is one obtained by coating the surface of a Cu ball with Sn plating, Ni plating, or Sn—Ag—Cu plating.
For example, Patent Document 1 discloses a ball for connection terminal formed by performing tin-silver-copper-containing plating on a spherical body made of a metal or an alloy and having a diameter of 10 to 1000 μm, the plating containing 0.5 to 3.4 mass % of silver, 0.3 to 0.8 mass % of copper and the remainder of substantially tin and inevitable impurities. Patent Document 2 discloses a ball for connection terminal which includes a base plating layer containing Ni on a surface of a Cu core ball with the diameter of 10-1,000 μm, and a plated soldering layer having the composition containing, by mass, 0.3-2.0% of Ag, 0.05-1.0% of Cu, the remainder of Sn and inevitable impurities on a surface of the base plating layer.
Further, as a joining member that maintains space between substrates, a joining member using a resin or the like as a core other than a joining member using a Cu ball as a core has been developed. Patent Document 3 discloses a conductive particle including a base particle made of a resin, a copper layer provided on a surface of the base particle, and a solder layer provided on a surface of the copper layer. Patent Document 4 discloses a conductive particle including a resin particle and a conductive layer provided on a surface of the resin particle.